The invention relates to a method of processing control instructions received from at least two identifiable sources via a communication connection. Such a method can be used, inter alia, in apparatuses which are coupled together by use of a bus. These may be audio and video apparatuses, but aim, for example washing machines, microwave ovens, luminaires and the like.
The invention also relates to an apparatus provided with a control circuit adapted to perform the method.
Lately, apparatuses have been provided with a connection for coupling them to a common bus. By use of this bus a plurality of apparatuses can be operated from one point in the house. It is also possible to transmit all kinds of control instructions from each apparatus to any other apparatus which is connected. An example of such a bus is known under the name of Domestic Digital Bus (frequently abbreviated to D2B bus) which is described, for example, in chapter 11 (The D2B Concept) of the User Manual of Single-Chip 8-bit Microcontrollers, published by Philips Electronic Components and Materials, 1986. The D2B bus provides easy operation of, for example, an audio/video system including a plurality of apparatuses. For example, a video recorder may automatically switch on a television receiver and tune this receiver to the correct video recorder channel when a video tape is to be displayed.
Apparatuses having a D2B connection will often also have their own infrared receiver so that they can also be used as stand-alone apparatuses. Such apparatuses may be implemented in such a way that a control instruction which has been received by the infrared receiver and cannot be carried out by the apparatus itself is passed on via the D2B bus to an apparatus which does have the required facilities. The latter apparatus then need not have an infrared receiver of its own, or it may be accommodated in a closed space. If more apparatuses having theft own infrared receivers are coupled together via the D2B bus, a problem arises which will now be illustrated with reference to an example. An audio/video system comprises a video recorder, a television monitor and an audio amplifier with loudspeakers. The video recorder, provided with an infrared receiver, receives the operating command "volume up" from an infrared transmitter for increasing the sound volume by one step, but it cannot carry out this command itself because it lacks a built-in audio amplifier section. The same applies to the television monitor which is also provided with an infrared receiver. In a previously performed installation phase both apparatuses have been programmed to pass on control instructions relating to sound functions via the D2B bus to the audio amplifier accommodated in a cabinet. The apparatuses will attempt to do this simultaneously or substantially simultaneously. In response to an arbitration procedure described in the Reference the two instructions will be passed on to the audio amplifier one after the other. The audio amplifier now receives the control instruction "volume up" from both apparatuses and will carry out the two instructions. The result is that the volume is raised by two steps, which may generally not have been the user's intention. If the user keeps the "volume up" key on the infrared hand-held remote control unit depressed, this operating command is generated in a repetitive manner and both apparatuses will pass on the corresponding control instruction also in a repetitive manner to the audio amplifier. The volume will now be raised twice faster than is desirable.
Apparatuses passing on a control instruction to another connected apparatus via the D2B bus will hereinafter be referred to as sources. The apparatus for which these control instructions are intended is provided with a control circuit receiving and processing the control instructions. It is to be noted that the control circuit can identify the source of a control instruction. For this purpose, and as indicated in the Reference, each "D2B message" on the bus does not only include the control instruction and a "slave address" (with which the apparatus is addressed) but also a "master address" which identifies the source of the message.